(a) Technical Field
The present invention relates to an on-board charger for charging a battery of an eco-friendly vehicle. More particularly, the present invention relates to an on-board charger for charging a battery of an eco-friendly vehicle, that reduces an output current ripple by improving a snubber circuit unit of an on-board charger for charging a battery in plug-in hybrid and electric vehicles.
(b) Background Art
Generally, plug-in hybrid vehicles and electric vehicles, types of eco-friendly vehicles, include an on-board charger and a battery for power charging. A method for charging a battery using the on-board charger includes applying a home alternating current (AC) power to the on-board charger installed within a vehicle, generating a charging current by converting AC power into direct current (DC) power, and applying the charging current generated in the on-board charger to a high voltage battery for charging.
To increase the stability of charging operation of the on-board charger for the high voltage battery and prevent the reduction of the lifespan of the high voltage battery, a surge voltage of a rectifier diode included in the on-board charger should be minimized and the ripple of an output current should be reduced. To accomplish this, the on-board charger includes a snubber circuit unit.
Hereinafter, typical circuit configuration and operation of the on-board charger including the snubber circuit unit will be described with reference to FIGS. 1 and 2.
A typical on-board charger includes a power factor compensator 10, a full bridge input unit 20, a main transformer 30, a rectifier diode 40, a snubber circuit unit 50, an output inductor 60, an output capacitor 70, and a high voltage battery 80. The power factor compensator 10 is connected to an AC normal power supply and increases the use of effective power by compensating for the power factor of an AC input current to be equal to the power factor of an input voltage. The full bridge input unit 20 is connected to change a DC input voltage into an AC voltage. The main transformer 30 boosts an output voltage with respect to the AC voltage from the full bridge input unit 20, and secures insulation between a high voltage and a vehicle body. The rectifier diode 40 converts the AC voltage boosted in the main transformer 30 into an AC voltage. The snubber circuit unit 50 removes a surged high voltage generated the rectifier diode 40 is turned off. The output inductor 60 converts the output voltage into a DC voltage with a ripple reduced together with the output capacitor 70, and simultaneously reduces noise. The output capacitor 70 converts the output voltage into the DC voltage with a ripple reduced together with the output inductor 60, and simultaneously reduces noise. The high voltage battery 80 is charged with the DC voltage from the output capacitor 70.
Particularly, a typical snubber circuit unit 50, as shown in FIG. 1, includes one diode D1, one capacitor C1, and one resistor R1 between the output terminal of the rectifier diode 40 and the input terminal of the output inductor 60. In other words, the diode D1 and the capacitor C1 of the snubber circuit unit 50 are sequentially disposed between the output terminal of the rectifier diode 40 and the input terminal of the output inductor 60, and the resistor R1 is connected to the capacitor C1. Accordingly, a surge voltage generated upon turning off the rectifier diode 40 is charged to the capacitor C1 via the diode D1 of the snubber circuit unit 50, and the surge voltage charged in the capacitor C1 is discharged and removed via the resistor R1. However, when a significant heat loss occurs in the resistor R1, the snubber circuit may be damaged by burning, resulting in the destruction of the whole circuitry.
Another typical snubber circuit unit 50, as shown in FIG. 2, includes two diodes D1 and D2 and one capacitor C1 between the output terminal of the rectifier diode 40 and the output terminal of the output inductor 60. In other words, the snubber circuit unit 40 includes the second diode D2 that applies a voltage while forming a closed section from the output terminal of the output inductor 60 to the capacitor C1, in addition to the first diode D1 and the capacitor C1 that are sequentially arranged between the output terminal of the rectifier diode 40 and the output terminal of the output inductor 60.
Accordingly, the surge voltage generated upon turning off the rectifier diode 40 is charged into the capacitor C1 (black arrow of FIG. 2), and the surge voltage charged in the capacitor C1 is discharged to the capacitor C1 via the output inductor 60 and the second diode D2 as indicated as the white arrow of FIG. 2. However, in addition to the ripple of the output inductor 60, a current generated by the resonance of the capacitor C1 and transformer leakage inductances is added to be output to the output capacitor 70, and thus the current ripple flowing in the inductor may increase and a Root Mean Square (RMS) current may increase in the output capacitor 70, thus shortening the lifespan of the capacitor. In addition, the battery lifespan may also be affected by the increase of the ripple current at the high voltage battery.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.